ACC rocks! I got the cut-pile with the MASS back... and if my floor would've been "correct," it would've dropped right in without any struggles.
BUT...
I had to replace the seat platforms when I replaced the floor pans. The only seat platforms out there are for coupes/'verts - no FBs yet. I did manage to cut them down a little, so they're somewhere between the coupe/'vert height & thickness and the FB. But did I stop there - Oh Heck No... being 6'5", I had this idea of moving the seat platforms back about 2" to give myself the luxury of a little bit more legroom without even giving the idea of installing molded carpet a second thought.
Yeah... what a PITA to get that stuff in there - being molded, it did not want to give itself up... but the heat gun helped a bit (don't use it too much and only on low settings). Don't get me wrong - it looks great and I love it, but my trying to get a little bit more for 'me' kinda messed things up, complications-wise.
Aside from that self-inflicted wound, I have nothing but good stuff to say about the ACC carpet I bought. I think if I do it again (ever), I'll go with non-MASS-backed, non-Mach 1 carpet - the vinyl "floor mat" inserts bug the crap out of me and make the floor mats slide around a little bit than I'd like.